1. Field of the Invention
The invention relates to a diagnostic system and method for an electric leak detecting device in a power supply unit having an electric leak detecting function.
2. Description of the Related Art
There are cases where an electric current from a direct current power supply (battery) leaks to a vehicle body (a ground fault occurs) due to causes such as a contact failure of a bus line. Therefore, an electric leak is detected by an electric leak detecting device. When an electric leak is detected, an alarm lamp of a meter lights up, or the like.
According to Japanese Patent Laid-Open Publication No. 8-70503, in order to detect an electric leak, a rectangular wave is input in between a battery and a motor via a resistance and a coupling capacitor which are connected in series. Based on the fact that a voltage between the resistance and the coupling capacitor fluctuates according to an electric leak state, the voltage is monitored such that an electric leak is detected by an electric leak detecting device.
According to Japanese Patent Laid-Open Publication No. 8-226950, a switch is turned ON via a capacitor and a resistance, which are connected in series, such that a battery is grounded for a predetermined time and the capacitor is charged. A voltage of the capacitor is monitored such that an electric leak is detected by an electric leak detecting device.
Each of the electric leak detecting device disclosed in Japanese Patent Laid-Open Publication No. 8-70503 and the electric leak detecting device disclosed in Japanese Patent Laid-Open Publication No. 8-226950 includes a capacitor, and determines whether an electric leak has occurred while maintaining an insulation state between the battery and the motor. Unlike these electric leak detecting devices, an electric leak detecting device disclosed in Japanese Patent Laid-Open Publication No. 10-221395 forcibly (artificially) grounds a battery terminal via a resistance and a switch, and performs a diagnosis of an operating state of the electric leak detecting device which detects a simulated electric leak (ground fault) state so as to perform a self-diagnosis of the operating performance thereof.
However, with the electric leak detecting devices disclosed in Japanese Patent Laid-Open Publication No. 8-70503 and Japanese Patent Laid-Open Publication No.8-226950, it is difficult to detect an electric leak when an electric potential (common mode voltage) of the battery terminal with respect to an electric potential of a vehicle body fluctuates. This is because a transitional charging/discharging current corresponding to the fluctuation of the electric potential is supplied to the capacitor, and therefore a signal for detecting an electric leak fluctuates. This phenomenon, which occurs in the electric leak detecting devices disclosed in Japanese Patent Laid-Open Publication No. 8-70503 and Japanese Patent Laid-Open Publication No. 8-226950, also occurs in the electric leak detecting device disclosed in Japanese Patent Laid-Open Publication No. 10-221395. Since a signal for detecting a simulated electric leak fluctuates, it is difficult to perform an accurate self-diagnosis.
Among the configurations disclosed in the above-mentioned publications, there is a configuration where the switch and a relay are provided between the battery and an inverter. Even in this case, a diagnosis of the operating performance of an electric leak detecting circuit is performed regardless of an ON/OFF state the relay and the like. Therefore, it is difficult to accurately perform a diagnosis of the operating performance of the electric leak detecting circuit disclosed in the publication.